It is a highly responsive and stable tuner, and the size, solid metal casing and LED lighting make it a great item that is easy to use and see on a dark stage. Having said that, the (defective?) unit I received makes very noticeable electronic noises when in tuning mode.
Stepping on the switch to engage the tuning mode cuts off the signal from the signal-out connection. There is no option to allow for tuning without cutting the signal, which is sometimes necessary in a live situation or due to the set up of your pedal signal chain.
As the LED lights switch on and off rapidly to display the graphical equivalent of a shifting needle on a tuning meter (to indicate your pitch) the unit buzzes, whizzes, hums and beeps like R2D2 -- only not nearly as cute. It would have been somewhat tolerable if I had the option to let the guitar signal through and perhaps hide those horrible noises, but I can't.
I had thought about returning this unit, but am now considering keeping it for its size, price, high responsiveness and LED-lighting feature. I will just have to go to the amp and turn off the standby switch every time I'm tuning. I haven't made up my mind yet *sigh*